1. Field of the Invention
The present invention relates generally to the field of magnetic data storage. In particular, the present invention relates to a thin film media having a tilted magnetic anisotropy for use in magnetic recording.
2. Description of the Relevant Art
Demands are currently being made to further increase the capacity of magnetic data storage. A major objective of research efforts in thin film magnetic materials is to make recording media with properties, which are suitable for recording at higher data densities. Achievement of higher recording densities is impaired by several problems. First, as the quantity of magnetic flux corresponding to the data becomes smaller, it becomes increasingly difficult to separate the data signal from the noise. Second, as the recording density increases without corresponding improvement in the materials, the super-paramagnetic limit of the materials is approached so that thermal energy can potentially randomize the data stored in the magnetic material. Both of these problems are related to the energy density associated with the magnetic anisotropy of the magnetic material, commonly quantified by the constant Ku for a particular material. Materials with higher Ku values are desired for recording media to avoid the problems above.
In materials with larger Ku values, the property of media coercivity (Hc) is also generally increased. Increased coercivity of the magnetic media in turn requires larger write field strength to be generated by the recording heads. The higher the coercivity the higher the required write field strength and hence the more difficult it is to successfully record data in the magnetic material.
A method proposed to overcome the problems of high write field strength requirements to write high Ku materials is to tilt the magnetization away from the surface normal in perpendicular recording or from the surface plane in longitudinal recording. For this proposal, media must be created where the angle between the direction of preferred magnetization (magnetic easy axis) and the surface normal falls between 0° (perpendicular media) and 90° (longitudinal media), also referred to as tilted media. Many attempts have been made to produce tilted media without success.
Several attempts to achieve a tilted media involved the processes of oblique deposition. Oblique deposition is defined as a deposition geometry where a beam of atoms or particles impinges upon the surface of a wafer at a defined angle. The angle is generally measured with respect to the surface normal. Oblique deposition of almost any magnetic material or deposition of a magnetic material onto any oblique deposited seedlayer will give some minimal degree of magnetic uniaxial reorientation likely due to either shape anisotropy, stress anisotropy or a combination of the two. Shape anisotropy and stress anisotropy are not intrinsic properties of the material. Shape anisotropy is due to a geometrically induced directional dependency of the demagnetization field within the material. Stress anisotropy is attributed to external physical forces compressing or stretching the material. However, shape anisotropy and stress anisotropy are both weak and thus the previous attempts have failed to produce tilted magnetic anisotropy greater than a few degrees.
The use of conventional underlayers or seedlayers with oblique deposition to achieve tilted media has been attempted. For example, an underlayer may be oblique sputter deposited producing a corrugated surface for deposition of additional media layers. These conventional structures rely primarily on combinations of shape and stress anisotropy arising from the elongated shape of the grains or uneven surfaces of a seedlayer to provide tilted magnetic anisotropy of only a few degrees. Additionally, the magnetic anisotropy is frequently limited to narrow ranges of layer thicknesses because stresses and structures within the material vary with the thickness of the deposited material. Consequently, there remains a need in the art for a magnetic media with a tilted magnetic anisotropy that is both of large enough degree and consistently controlled so as to be suitable for use in high-density recording.